1. Field of the Invention
The present invention relates to an ion removing apparatus capable of removing ions from the liquid, and, more particularly, to a capacitive deionization (CDI) apparatus capable of removing ion components from the liquid using electrical and chemical methods.
2. Description of the Related Art
Among various methods used to purify water containing salt components or heavy metals, a method using ion exchange resin is widely used. However, the method using ion exchange resin is uneconomical in that an acid or base solution should be used in the regeneration of resin and a large amount of polymer resin and chemicals should be used to process a large amount of water.
Recently, a lot of research has been done on a capacitive deionization (CDI) apparatus to overcome the disadvantages.
The capacitive deionization (CDI) technology is based on a simple principle in which anions are electrically adsorbed to a positive electrode and cations are electrically adsorbed to a negative electrode by applying a voltage between two porous carbon electrodes formed in a stack shape to remove ions dissolved in a fluid such as water. Further, when ions adsorbed to the electrodes are saturated, the regeneration of the electrodes can be easily performed by switching the polarity of the electrodes or by cutting off the power supply. Since a cleaning solution (acid, base or the like) is not used for the regeneration of the electrodes as opposed to an ion exchange resin method or a reverse osmosis, there is no subsidiary chemical waste. Further, since the corrosion or contamination of the electrodes hardly occurs, the CDI apparatus has a semi-permanent life span. Also, since energy efficiency is high, energy consumption can be reduced by 90˜95% in the CDI technology compared to other processing methods.
An example of the CDI apparatus is disclosed in U.S. Pat. No. 6,309,532.
The CDI apparatus disposed in the patent includes end plates provided at upper and lower ends; a number of electrodes, current collectors, and insulating materials forming a middle layer; and bolts, nuts and sealing to fasten the components; and the like.
The electrodes mainly employ a carbon material having pores with a high specific surface area. The electrodes are adhered to the collector using a conductive material. The collector is made of a material such as a titanium sheet or a carbon foil having good electrical conductivity. A channel is formed at a specific portion of the collector to form a flow path and the electrodes are attached to the opposite surfaces of the collector, thereby forming a single electrode body. However, the uppermost collector and the lowermost collector have a single electrode attached to one surface thereof.
In the CDI apparatus disposed in the patent, a CDI stack is formed by alternately stacking the electrodes, collectors, insulating materials and sealing and fastening them. In the CDI stack, when positive (+) and negative (−) voltages are alternately applied to the electrodes and water flows into an upper or lower inlet, the water moves in a zigzag through channels formed on the collectors and ion components included in the water are adsorbed to the carbon material of the electrodes. After a specific level of adsorption is performed, a negative (−) voltage is applied to the positive electrode and a positive (+) voltage is applied to the negative electrode, ion components adsorbed to the carbon material are removed and the regeneration of the electrodes is simply achieved.
However, in the CDI apparatus disposed in the patent, the carbon material and the collector are adhered to each other using conductive epoxy or the like in the manufacture of the electrodes. Accordingly, the pores of the carbon material may be partially clogged and electrical conductivity may deteriorate due to contact resistance.
Further, since each layer is sealed using a gasket made of rubber or Teflon, when a number of cells are stacked and fastened to each other, upper, middle and lower cells cannot be fastened with a uniform force. Accordingly, since the cells are spaced by different distances, a uniform voltage cannot be applied to the cells. As a result, ion removal efficiency decreases in some cells.
Further, titanium or metal having the same function is used as the collector. In this case, the manufacturing cost increases. If other metals are used to reduce the manufacturing cost, the metals may be corroded. Further, in a case of using an inexpensive carbon foil, since the boundary of the collector is exposed to the outside in the structure disposed in the patent, there is a problem that the collector may be damaged.